1. Field of the Invention
This invention relates generally to pressforming a container, and more specifically to the method and apparatus used to manufacture an articulable clamshell container from a paperboard material.
2. Description of the Related Art
Clamshell containers, particularly those made from paperboard or corrugated materials, have long been known and used for packaging of various foods such as hamburgers, carry out meals, sandwiches, etc. They are desirable because they are a single piece structure which can be latched closed to enclose a food product and separate it from other contained food products in a sack or other wrap. Clamshell containers maintain the temperature and cleanliness of the food product and prevent the enclosed food product from contacting and possibly staining surrounding objects.
One type of clamshell containers is traditionally made from flat blanks that must be cut, creased (scored), and eventually folded and glued or interlocked into shape. However, these require many steps in their manufacturing process, making the process inefficient and costly and they provide a clamshell container which is not aesthetically pleasing, has openings which allow leakage and is subject to the disengagement of its interlocking parts. Such a clamshell container is shown in U.S. Pat. No. 5,205,476 to Sorenson.
Another known method of manufacturing a clamshell container involves a two-step process of first scoring the paperboard and then pressforming the paperboard into the container shape by the application of pressure and heat. Clamshell containers of this type are illustrated in U.S. Pat. No. 5,577,989 to Neary, U.S. Pat. No. 4,778,439 to Alexander, and U.S. Pat. No. 6,415,944 to Toussant.
The first step of scoring or creating a score line in the flat paperboard creates weakened lines or creases in the paperboard so that the material will fold in the preselected locations. A scoring tool, separate from the pressforming machine, has traditionally made the score lines when the sheet material is flat and before pressforming. Scoring tools are typically called “Diecutters”, “Cutter/Creasers”, or “Diecutting Machines
The second step of pressforming or thermoforming the paperboard material in a die, forms the three dimensional contours of the clamshell container. Traditionally, the paperboard material is compressed between mating male and female dies of a die press. The deformation of the material is retained when the dies are withdrawn from the blank, so that the container retains its shape. This process forms a container having a continuous bottom and top portion, each of which have no openings around their sidewalls
There are, however, some problems associated with the traditional manufacturing process. One problem arises because the workpiece of corrugated paperboard must be moved from the scoring tool to the die press. This presents a registration problem when inserting the scored paperboard sheet into the die press forming machine. It is imperative to bring the scored paperboard sheet into registration with the press forming dies so that the contour shaped by the dies is in proper alignment with the scores of the paperboard sheet. Should the scored paperboard sheet be out of registration with the dies, even by a small amount, the resulting container will have the scored lines in the wrong place with respect to the contour of the container so the container will not fold properly and therefore the two halves of the clamshell container will not meet in proper registration.
In addition, the conventional method of scoring the paperboard material prior to the pressforming process is deficient when drawing the material into shapes with steep sidewall angles, those deeper than a standard paper plate. As the material draws into the mold, the pre-scored lines intended to become the lines of weakness, about which the container will be folded to make a clamshell, can be smoothed out or disappear under the forming pressure, which reduces the relative weakness of the score line relative to the neighboring material. As a result, the fold lines are deformed making it difficult to fold the container along the original pre-scored fold lines.
Two U.S. Patents attempt to reduce the difficulties associated with manufacturing this type of container, U.S. Pat. No. 4,256,025 to Goda et al. and U.S. Pat. No. 5,904,643 to Seeberger et al. Goda discloses an apparatus for pressforming a hinged container requiring multiple steps for forming the container. Seeberger describes an apparatus for forming containers, in which the paper is first scored to define the shape of the container and thereafter, the scored stock is simultaneously cut and formed into a container. Neither of the processes described in these patents overcome the problems discussed above, including the problem of flattening the score lines during pressforming.
Therefore, it is an object and feature of the invention to provide an apparatus and a method for simultaneously forming creases in the paperboard while the paperboard is undergoing the pressforming process.
It is another object and feature of the invention to provide a method that reduces the inefficiency and reduces the cost of manufacturing a clamshell container.